A 20-foot-by-20-foot hole in the roof of an underground rail tunnel at the Hanford Site, a former nuclear production facility that is now contaminated, has caused some employees to be evacuated. The Department of Energy says that surveys show "no indication of release of contamination."

Department of Energy

Originally published on May 10, 2017 4:02 pm

Updated at 5:45 p.m. ET

The Department of Energy has declared an emergency at a nuclear-contaminated site in Washington state, after soil caved in over a portion of a tunnel containing rail cars contaminated with nuclear waste.

"All personnel in the immediate area have been accounted for — they are safe — and there is no evidence of a radiological release," Destry Henderson, spokesperson for the Hanford site's emergency operations center, said in a brief statement on Facebook.

Some employees were evacuated and others were told to move indoors as a "precaution," officials say. Anna King of the Northwest News Network, a public radio station collaboration, reports that approximately 3,000 other workers in the area were originally taking cover indoors. Nonessential employees have since been sent home, and essential employees were instructed to avoid the site of the tunnel.

There are no reports of injuries.

The Hanford Site, about 150 miles southeast of Seattle, is a former nuclear production complex and home to a long-running, challenging and sometimes troubled cleanup operation.

It's generally regarded as the most contaminated nuclear site in America. The Department of Energy says it's the most challenging of the government's nuclear cleanup projects, with millions of tons and hundreds of billions of gallons of nuclear waste.

The Department of Energy says a 20-foot-by-20-foot section of soil caved in where two underground tunnels meet next to the Plutonium Uranium Extraction Facility, known as the PUREX plant. The cave-in was discovered during routine surveillance.

The tunnels in question were storing rail cars that once carried radioactive nuclear fuel from reactors to production facilities, back when the site was still used to manufacture nuclear weapons. Each tunnel is hundreds of feet long, the Hanford Site says, made of wood and concrete and covered with about 8 feet of soil. A 20-foot-long section appears to have collapsed.

"There is no indication of a release of contamination at this point," the Department of Energy says.

"Officials continue to monitor the air and are working on how they will fix the hole in the tunnel roof," the Hanford Emergency Information site announced. "They are looking at options that would provide a barrier between the contaminated equipment in the tunnel and the outside air that would not cause the hole in the tunnel's roof to widen."

The site of the collapse had been previously identified as a potential hazard, the Northwest News Network writes:

"Between 1960 and 1965, eight rail cars were pushed inside one tunnel, full of radioactive waste. Another tunnel was constructed in 1964 to hold 40 additional railcars."

The governor of Washington, Jay Inslee, says there are "many questions" about how the collapse happened, reports member station Oregon Public Broadcasting.

"We'll have to get to the bottom of that," he said. "At the moment we're focusing on the safety of workers and making sure there's no release beyond [the] immediate site."

OPB described the Hanford site, and the challenges of cleaning up nuclear waste, late last year, as part of a project about the environmental impact of the U.S. military in the Northwest:

"Hanford is the nation's largest nuclear cleanup site, with 56 million gallons of radioactive waste sitting in old, leaky underground tanks just a few hours upriver from Portland. After more than 20 years and $19 billion[,] not a drop of waste has been treated.

"Hanford sits next to the Columbia River. It was one of the original Manhattan Project sites. Its nine nuclear reactors irradiated uranium fuel rods. That created plutonium, which was extracted with chemicals, processed and shipped to weapons factories. Each step produced radioactive waste. ...

"The stored waste has to be treated in special rooms called black cells, which are too radioactive for humans to enter. The machinery in these black cells is supposed to operate for 40 years with no direct human intervention. If something goes wrong, the cells could be damaged."

The treatment plant was originally supposed to be finished in 2007, but the deadline has been extended several times, OPB reports.